Acid catalyzed reactions are important reactions in the rearrangement and conversion of hydrocarbons. Such acid catalyzed reactions include isomerization, alkylation, acylation, transalkylation of alkylaromatics, hydration of olefins, dehydration, dehydrohalogenation, oligomerization and polymerization, esterification, hydrolysis, catalytic cracking, catalytic reforming, oxidation, and aldol condensation. Historically, the acid catalysts themselves are often solid acids, and can be of many forms. Solid acids have been disclosed in the form of, e.g., amorphous mixed metal oxides, zeolites, clays, pillared clays, and in the form of functionalized organic polymer gels, and inorganic polymer gels with functionality grafted onto the surface. This invention concerns the last two types of solid acids listed. Solid acids also find use as cation exchange resins, especially where such materials are not strong enough as an acid to function as a catalyst.
An extremely important part of a solid acid is the support to which the functionality is attached. This invention creates a whole new type of solid acids by directly functionalizing an organic-inorganic hybrid whose framework acts as a support for acidic groups. The situation is somewhat analogous to, but a step forward from, organic resins having a polymer backbone to which are attached groups bearing an acid functionality. Organic-inorganic hybrid materials are disclosed in Shea, K. J., and Loy, D. A. Chemistry of Materials 1989; Shea K. J., Loy D. A., and Webster O. J. Am. Chem. Soc. 1992, 6700-6710 pp.; Shea, K. J., Loy, D. A., Webster, O. Mater. Res. Soc. Symp. Proc. Vol 180 Better Ceram. Chem 1990, 975-80 pp.; Shea, K. J., Loy, D. A., and Webster O. Polym. Mater. Sci. Eng. Vol 63 1990, 281-5 pp. This art teaches that organic groups can be introduced at regular intervals in an inorganic silicate framework, thus forming a three-dimensional organic-inorganic hybrid silicate-like polymeric material, also called an organically-bridged polysilsesquioxane. A two-dimensional representation of the well-known inorganic silicate framework is shown in l, and an analogous representation of the organically-bridged polysilsesquioxane where the represents the organic group is shown in II. Of course, the frameworks I and II, in reality, extend to form a three-dimensional, continuous, amorphous solid. ##STR1## One stated objective of the disclosed work was to provide molecular level control of the morphology of the framework, another was to provide a new chromatographic support, and a third was use in optical applications. However, the current invention furnishes an entirely new twist. By choosing specific types of organic groups to be introduced into the three-dimensional silicate-like framework, and then taking advantage of the reactivity of those organic groups to add acid functionality, this invention presents a whole new type of solid acids which can be used as, for example, catalysts or cation exchange materials.
The present invention solves several problems with solid acids currently in the art. For example, with completely inorganic solid acids, one is limited as to what functionality may be incorporated onto the solid acid. The present invention opens up the choices by allowing a wide variety of acid functionalities to be incorporated due to the reactivity of the organic groups within the framework of the solid acid. Furthermore, the instant invention also provides advantages over completely organic solid acids. The inorganic portion of the present invention affords greater thermal stability, structure stability, and porosity over strictly organic acids. Moreover, the aryl-bridged polysilsesquioxanes provide increased dimensional stability as compared to fully organic acids.
As the above solutions to long standing problems of current acid catalysts suggest, combining the benefits of acid functionality and inorganic polymeric supports is desirable and the prior art shows others have pursued this goal. For example, a relevant published French patent application (2 669 033) discloses an acid catalytic composition comprising a small molecular weight inorganic polymer with sulfonated aryl pendant groups which is grafted onto a completely inorganic support. This acid catalyst is then used in the published French patent application (2 669 021 ) in a preparation of tertiary olefins. The structure is shown below where M is an inorganic oxide, mixture of inorganic oxides, or an inorganic oxide bearing surface hydroxyl groups, and/or silylalkoxy groups of formula --Si--(OR.sup.2).sub.3 where each R.sup.2 is alkyl; R.sup.1 is a divalent group of the formula .dbd.Si--(R.sup.3 R.sup.4) where R.sup.3 is halogen, alkyl, or alkoxy and R.sup.4 (which can be the same as or different from R.sup.3) is alkyl or alkoxy; p is 0 or 1; Y is an hydroxyl group or bond with inorganic support; Y.sup.1 and Y.sup.2 are each hydrogen or a group of the formula --Si(R.sup.7).sub.3 where each R.sup.7 is alkyl; A.sup.1 and A.sup.2 are each 6-30 carbon arylsulphonic groups containing 1 or more sulphonic groups or one or more of these substituted by at least one halogen and or at least one 1-5 carbon haloalkyl containing 1 or more halogen atoms and or at least one NO.sub.2 ; n is 5-10,000. ##STR2## Similarly, as exemplary of work in the art, Shon, J. R., Journal of Molecular Catalysis Vol 62, 1990, discloses using esterification and then sulfonation to react pendant "benzenesulfo groups" onto a completely inorganic silica support. Specifically, Shon disclosed the pendant groups ##STR3## attached to an inorganic silica support. A critical distinction between the prior art and the subject invention is that in the prior art the acid functionality was added to pendant organic groups while in the instant invention the organic groups bearing acid functionality are part of the backbone of the support structure itself, thereby forming an organic-inorganic hybrid polymeric support. See also, U.S. Pat. No. 4,426,508 where an inorganic mineral support is coated with a film of polymeric material comprising pendant sulfonic or phosphonic acid groups.
While Shea et. al. above disclosed the formation of organically-bridged polysilsesquioxanes, and others have attached acid functionalized groups to organic pendant groups pendant to an inorganic polymer, applicants here are the first to recognize and create acid catalysts where the acid functionality is incorporated within an organic-inorganic hybrid silicate-like framework.